I'd like to see some of his work. It sounds interesting. The camera is just an artistic tool. The artist can use it any way he wants to achieve his vision. I think MattKing's question is the best one. If your son likes what he is getting and means what he gets, it is right.
Most good advice already posted so i will just add, be happy that you have a 21 year old soon that is into LF photography or at least taking a peak at it. Be supportive and perhaps let him know how you would see this scene but let him explore and learn. One day he may tell you. See i told you this would sell.
I'm surprised a bit. Perhaps his is the "Right" way and you've been pretty plain and "wrong" all these years. Art is VERY objective and you should be teaching him this. You asked.
I would hit him with a stick and tell him "its my way or the highway". That will take care of it. You won't have to worry about it anymore. (sounds like he is having fun)
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Yes, he recognizes that the images he made are "twisted". He likes that. Imagine a cone shaped building whose image on a 4x5 negative is mostly out of focus except for a narrow horizontal band in the middle that is tack sharp. I've held my opinion in, knowing he is exploring his own vision.
I know ONE professor of Photo in a major university somewhere near you who does just that kind of thing now and then. So, maybe he's working on his admissions portfolio.